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SubjectRe: [PATCH v2] mac80211: fix race in ieee80211_register_hw()
On Tue, Apr 7, 2020 at 3:41 PM Sumit Garg <sumit.garg@linaro.org> wrote:
>
> A race condition leading to a kernel crash is observed during invocation
> of ieee80211_register_hw() on a dragonboard410c device having wcn36xx
> driver built as a loadable module along with a wifi manager in user-space
> waiting for a wifi device (wlanX) to be active.
>
> Sequence diagram for a particular kernel crash scenario:
>
> user-space ieee80211_register_hw() ieee80211_tasklet_handler()
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> | | |
> |<---phy0----wiphy_register() |
> |-----iwd if_add---->| |
just a nitpick, a better one would be (iwd: if_add + ap_start) since
we need to have 'iwctl ap start'
to trigger the interrupts.
> | |<---IRQ----(RX packet)
> | Kernel crash |
> | due to unallocated |
> | workqueue. |
> | | |
> | alloc_ordered_workqueue() |
> | | |
> | Misc wiphy init. |
> | | |
> | ieee80211_if_add() |
> | | |
>
> As evident from above sequence diagram, this race condition isn't specific
> to a particular wifi driver but rather the initialization sequence in
> ieee80211_register_hw() needs to be fixed. So re-order the initialization
> sequence and the updated sequence diagram would look like:
>
> user-space ieee80211_register_hw() ieee80211_tasklet_handler()
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> | | |
> | alloc_ordered_workqueue() |
> | | |
> | Misc wiphy init. |
> | | |
> |<---phy0----wiphy_register() |
> |-----iwd if_add---->| |
same as above.
> | |<---IRQ----(RX packet)
> | | |
> | ieee80211_if_add() |
> | | |
>
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Sumit Garg <sumit.garg@linaro.org>
> ---
>
> Changes in v2:
> - Move rtnl_unlock() just after ieee80211_init_rate_ctrl_alg().
> - Update sequence diagrams in commit message for more clarification.
>
> net/mac80211/main.c | 22 +++++++++++++---------
> 1 file changed, 13 insertions(+), 9 deletions(-)
>
> diff --git a/net/mac80211/main.c b/net/mac80211/main.c
> index 4c2b5ba..d497129 100644
> --- a/net/mac80211/main.c
> +++ b/net/mac80211/main.c
> @@ -1051,7 +1051,7 @@ int ieee80211_register_hw(struct ieee80211_hw *hw)
> local->hw.wiphy->signal_type = CFG80211_SIGNAL_TYPE_UNSPEC;
> if (hw->max_signal <= 0) {
> result = -EINVAL;
> - goto fail_wiphy_register;
> + goto fail_workqueue;
> }
> }
>
> @@ -1113,7 +1113,7 @@ int ieee80211_register_hw(struct ieee80211_hw *hw)
>
> result = ieee80211_init_cipher_suites(local);
> if (result < 0)
> - goto fail_wiphy_register;
> + goto fail_workqueue;
>
> if (!local->ops->remain_on_channel)
> local->hw.wiphy->max_remain_on_channel_duration = 5000;
> @@ -1139,10 +1139,6 @@ int ieee80211_register_hw(struct ieee80211_hw *hw)
>
> local->hw.wiphy->max_num_csa_counters = IEEE80211_MAX_CSA_COUNTERS_NUM;
>
> - result = wiphy_register(local->hw.wiphy);
> - if (result < 0)
> - goto fail_wiphy_register;
> -
> /*
> * We use the number of queues for feature tests (QoS, HT) internally
> * so restrict them appropriately.
> @@ -1207,6 +1203,8 @@ int ieee80211_register_hw(struct ieee80211_hw *hw)
> goto fail_rate;
> }
>
> + rtnl_unlock();
> +
> if (local->rate_ctrl) {
> clear_bit(IEEE80211_HW_SUPPORTS_VHT_EXT_NSS_BW, hw->flags);
> if (local->rate_ctrl->ops->capa & RATE_CTRL_CAPA_VHT_EXT_NSS_BW)
> @@ -1254,6 +1252,12 @@ int ieee80211_register_hw(struct ieee80211_hw *hw)
> local->sband_allocated |= BIT(band);
> }
>
> + result = wiphy_register(local->hw.wiphy);
> + if (result < 0)
> + goto fail_wiphy_register;
> +
> + rtnl_lock();
> +
> /* add one default STA interface if supported */
> if (local->hw.wiphy->interface_modes & BIT(NL80211_IFTYPE_STATION) &&
> !ieee80211_hw_check(hw, NO_AUTO_VIF)) {
> @@ -1293,6 +1297,8 @@ int ieee80211_register_hw(struct ieee80211_hw *hw)
> #if defined(CONFIG_INET) || defined(CONFIG_IPV6)
> fail_ifa:
> #endif
> + wiphy_unregister(local->hw.wiphy);
> + fail_wiphy_register:
> rtnl_lock();
> rate_control_deinitialize(local);
> ieee80211_remove_interfaces(local);
> @@ -1302,8 +1308,6 @@ int ieee80211_register_hw(struct ieee80211_hw *hw)
> ieee80211_led_exit(local);
> destroy_workqueue(local->workqueue);
> fail_workqueue:
> - wiphy_unregister(local->hw.wiphy);
> - fail_wiphy_register:
> if (local->wiphy_ciphers_allocated)
> kfree(local->hw.wiphy->cipher_suites);
> kfree(local->int_scan_req);
> @@ -1353,8 +1357,8 @@ void ieee80211_unregister_hw(struct ieee80211_hw *hw)
> skb_queue_purge(&local->skb_queue_unreliable);
> skb_queue_purge(&local->skb_queue_tdls_chsw);
>
> - destroy_workqueue(local->workqueue);
> wiphy_unregister(local->hw.wiphy);
> + destroy_workqueue(local->workqueue);
> ieee80211_led_exit(local);
> kfree(local->int_scan_req);
> }
> --
> 2.7.4
>


--
Thanks,
Regards,
Chaitanya T K.

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